1. Field of the Invention
The present invention relates to apparatus and methods for generating a defined environment for particle-shaped samples, and in particular for particle-shaped samples having to be kept in an environment of defined humidity, such as protein crystals.
2. Description of the Related Art
The protein crystallography is a method of structural analysis of proteins in which these are exposed to X-ray or synchrotron radiation in order to explore the molecule structure from diffraction images. By the attachment of irregularly shaped proteins in a protein crystal, channels develop which are filled with crystallization solution. Protein crystals are very sensitive due to the high solvency content as well as by the weak contacts in comparison with crystals of small molecules and are only stable in a special environment.
In order to guarantee such a stable environment, previously protein crystals, together with some mother liquor, i.e. the solution in which the crystal has grown, are mounted in a glass capillary, which is then closed at both ends. Thus, in the capillary, an atmosphere arises, in which the crystal may be kept. This procedure, however, is disadvantageous, because it is a closed system, so that manipulations at the crystal are no longer possible. Furthermore, it is known to subject protein crystals to quick-freezing in a so-called loop representing a loop fixture and to measure same at low temperatures. Apart from temperature annealing, the crystal can also no longer be manipulated here.
Recently systems have become known, in which protein crystals are kept stable in a humid airflow, wherein by the adjustment of the humidity of the airflow the relative humidity at the crystal may be checked in a simultaneous analysis of the crystal state at an X-ray camera.
Such systems are known for example in Reiner Kiefersauer et al., “Free-mounting system for protein crystals: transformation and improvement of diffraction power by accurately control humidity changes”, J. Appl. Cryst. (200), 33, pp. 1223-1230, and EP-A-0987543. These known systems include a measuring head including both a fixture for a protein crystal to be examined and a gas channel for feeding a humid air flow to the protein crystal. In these known systems, the humidity of the airflow is adjusted using a humidity regulation system, in order to adjust the mixing ratio of a dry airflow and a wet airflow depending on the humidity detected by means of a humidity sensor, in order to thus regulate the humidity of the airflow.
A similar method of adjustment of the humidity is also known in R. Kiefersauer et al., “Protein-Crystal Density by Volume measurement and Amino-Acid Analysis”, J. Appl. Cryst. (1996), 29, pp. 311-317. In T. Sjögren et al., “Protein crystallography in a vapour stream: data collection, reaction initiation and intermediate trapping in naked hydrated protein crystals”, J. Appl. Cryst. (2002), 35, pp. 113-116, there is also described a system for protein crystallography in a humid airflow. In this known system a bubbler is used to impart the gas with a desired humidity. In this, the gas is let to rise through a liquid, wherein the humidity of the gas may be manipulated by changing the temperature of the liquid or by changing the composition thereof. The gas with the humidity so adjusted is fed via a buffer vessel to a nozzle, at the outlet end of which a crystal is arranged at a fixture, so that a laminar gas flow strikes the crystal.
The known systems for adjusting the humidity of a gas flow are disadvantageous in that exact adjustment of the humidity, in particular in an interesting range slightly below 100% relative humidity, is difficult to realize therewith. In the methods mentioned first, using a humidity sensor, the employment of the sensor for the measurement of the relative humidity directly at the measurement location for the regulation of a humidifying means is not possible due to the spatial closeness at the crystal. Moreover, commercially available relative humidity sensors do not have sufficient accuracy and long-term stability in the required humidity range.